The embodiments described herein relate generally to circuit fault detection and, more particularly, to detecting a ground fault in a circuit.
In a conventional electrical system, analysis of sinusoidal AC current and voltage performance is simplified by using a phasor characterization of the sinusoids. Such phasor characterizations generally use complex numbers having “real” components associated with resistive elements and “imaginary” components associated with reactive elements. For example, a phasor characterization of a ground fault current in a circuit includes a reactive, imaginary current component that flows through the capacitive elements of the electrical system, and a resistive, real current component. The reactive current component is purely reactive and neither causes heating nor presents a shock hazard. Therefore, the reactive current component of the ground fault current does not necessitate tripping of a protective device. In contrast, the resistive component can cause heating and present a shock hazard. Accordingly, only the resistive of the ground fault current necessitates tripping of the protective device.
At least some known systems and devices for use in charging an electric device, such as an electric vehicle or hybrid-electric vehicle, are incapable of discriminating between capacitive-generated leakage current and resistive ground current. Accordingly, at least some known systems and devices are susceptible to nuisance tripping, which interrupts current flow to the electric device. For example, a charging system or device generally connects to a power distribution network through a household wall power outlet, such as an outlet that is provided in a garage or carport. Most fire codes and regulations require these outlets to include a ground fault circuit interrupt (GFCI) breaker or to use a self-contained ground fault interrupt wall outlet that detects resistive current. However, many electric vehicle on-board battery chargers generate a high leakage current that can cause a GFCI device, such as a GFCI breaker or a GFI wall outlet, to trip due to a capacitive current and when a true resistive ground fault is not actually present. At least some GFCI devices can be made to nuisance trip by a capacitive current to ground in the absence of a real, or resistive, ground fault condition. For example, the capacitive current can exceed a predetermined current threshold of at least some known GFCI devices and result in a nuisance trip of the GFCI device.